This topic caught my attention today, and I thought I would ask the wider community their thoughts.

Today's speaker talked about her research in lady beetles, and evaluating different diets for these beetles. She found that the "best" diet of aphids gave her a ratio of 30% female, 70% male from the viable eggs. (I even asked her after the talk if I understood her correctly.)

She didn't do any additional research into this, but is aware of other studies that found skewed ratios attributable to diet/nutrition or maternally-inherited cytoplasmic factors. I did some looking and found info on spirochete infection and selective death of males that shifted to population to female and this paper(Matsuka et al.).

What do you think could be influencing the shift to male in this population?

-lab rat-

Female Aphids are capable of parthenogenesis (only daughters produced) so perhaps the eggs are largely male so that the population can balance out.

-bob1-

I dont know a lot about this, but this is an intersting topic.

And I think its not weird at all there are factors influencing the male/female ratio. Take for example turtles: the male/female ratio in influenced by a small thing as temperature...

An other examples: there are bacteria out there "killing" male insects... and influencing the male/female ratio so that there are almost no males left... (as you allready mentioned)

Or what about the fact that some pesticides/herbicides also influence the male/female ratio.. (there are some pesticides out there killing males.. and not females for example)

And many other examples...

So I can imagine there is a influence of the diet.
(or maybe because a factor giving with the diet: example a chemical that is in/on the food for example...?)

Or maybe its just because of the male killing bacteria that the beetles start producing more males.
(check http://www.nature.com/hdy/journal/v84/n5/full/6887100a.html, I can imagine that the beetles adapt and start making more males, we dont know how she did the experiment? Maybe she had infections or started with beetles that were allready adapted to the male killing? Did she use the same beetles for the different diets for example? or did she use different beetles for each diet? This can influence the results I think... and the diet itself: maybe the "best" diet is a diet that causes stress/malnutrition or something else that shifts the ratio?)

Or maybe even this one (links food with the act of sex): Mating refusal and its significance in females of the ladybird beetle, Harmonia axyridis by SHOHKO OBATA , Physiological Entomology
Volume 13, Issue 2, pages 193–199, June 1988)

-pito-

bob1 on Fri Apr 29 04:53:47 2011 said:

Female Aphids are capable of parthenogenesis (only daughters produced) so perhaps the eggs are largely male so that the population can balance out.

But this is alternation of generations. During summer only females are produced by parthenogenesis. Males appear only in autumn to fertilise the winter eggs in holocyclic populations. I.e. eggs are also only produced for overwintering (more cold hardy), and females emerge then in spring for anholocyclic summer population development (parthenogenetically).

But that was anyway not the question. If I remember right there can be a quite large size difference between male and female Coccinelids. Changing sex rations were then related to available food for larvae, with favouring smaller males when food is scarce. But also other external factors as mentioned by pito play their role of course. I'm not sure if Wolbachia infections occur in ladybeetles, but why not?

-hobglobin-

An interesting topic, indeed. I talked to the speaker, who said that her advisor didn't let her investigate any of those options. She wanted to do nutritional analysis on the aphids, but since no one on her committee had any "molecular" experience, she wasn't allowed to do it. (We couldn't figure that out either.) She didn't note any sex-specific consumption of the different aphid species provided to her colony. She did note, however, that the introduced aphid was the best diet for the native ladybeetles.